Mental health in autistic adults: A rapid review of prevalence of psychiatric disorders and umbrella review of the effectiveness of interventions within a neurodiversity informed perspective

Background Autistic adults have high risk of mental ill-health and some available interventions have been associated with increased psychiatric diagnoses. Understanding prevalence of psychiatric diagnoses is important to inform the development of individualised treatment and support for autistic adults which have been identified as a research priority by the autistic community. Interventions require to be evaluated both in terms of effectiveness and regarding their acceptability to the autistic community. Objective This rapid review identified the prevalence of psychiatric disorders in autistic adults, then systematic reviews of interventions aimed at supporting autistic adults were examined. A rapid review of prevalence studies was completed concurrently with an umbrella review of interventions. Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines were followed, including protocol registration (PROSPERO#CRD42021283570). Data sources MEDLINE, CINAHL, PsycINFO, and Cochrane Database of Systematic Reviews. Study eligibility criteria English language; published 2011–2022; primary studies describing prevalence of psychiatric conditions in autistic adults; or systematic reviews evaluating interventions for autistic adults. Appraisal and synthesis Bias was assessed using the Prevalence Critical Appraisal Instrument and AMSTAR2. Prevalence was grouped according to psychiatric diagnosis. Interventions were grouped into pharmacological, employment, psychological or mixed therapies. Strength of evidence for interventions was assessed using GRADE (Grading of Recommendations, Assessment, Development and Evaluation). Autistic researchers within the team supported interpretation. Results Twenty prevalence studies were identified. Many included small sample sizes or failed to compare their sample group with the general population reducing validity. Prevalence of psychiatric diagnoses was variable with prevalence of any psychiatric diagnosis ranging from 15.4% to 79%. Heterogeneity was associated with age, diagnosis method, sampling methods, and country. Thirty-two systematic reviews of interventions were identified. Four reviews were high quality, four were moderate, five were low and nineteen critically low, indicating bias. Following synthesis, no intervention was rated as ‘evidence based.’ Acceptability of interventions to autistic adults and priorities of autistic adults were often not considered. Conclusions There is some understanding of the scope of mental ill-health in autism, but interventions are not tailored to the needs of autistic adults, not evidence based, and may focus on promoting neurotypical behaviours rather than the priorities of autistic people.

Introduction Mental ill-health is a common experience for autistic adults [1]. The recent Lancet Commission on autism research described a 'deep scarcity' of evidence regarding interventions and supports for this population [2,3]. Considering the recent increase in interest in outcomes for autistic adults, research and policy advancements in this field are urgently required.
There is a known increased risk for experiencing mental ill-health in autism this varies widely in terms of reported prevalence [3]. Estimated prevalence of autism in adults aged 16-64 years in UK is 2.9% [95% CI 2.7, 3.1] [4]. Prevalence of autism is 3.46 times higher for boys [5]. Autistic people have a wide range of needs which vary depending on environment, and co-occurrence of intellectual or physical factors, sensory factors, co-occurring neurodevelopmental differences, intellectual disabilities, or other psychiatric diagnoses [6][7][8]. Autistic people, and people with intellectual disabilities have more mental and physical needs than other people [9], and research indicates that needs prevalence will be even higher for people with cooccurring autism and intellectual disability [8].
Whilst there has been previous consideration of prevalence of psychiatric disorders in autistic populations [11], there is a need to distinguish between adult and child populations. Further consideration of the measurement tools used with autistic adults is also required to ensure that they are validated for this population [12]. The significance of co-occurring mental ill-health was identified in research which demonstrated that that up to 66% of autistic adults without intellectual disability have contemplated suicide compared to 17% of non-autistic adults, and research has linked this to social camouflaging [13].
Mental health has been identified as a top priority research area for autistic adults [14]. Mental health is a state of well-being in which an individual realises his or her own abilities, can cope with the normal stresses of life, can work productively and is able to make a contribution to his or her community [15]. As understanding of mental health in autism evolves, it is also recognised that personal factors cannot be separated from environmental factors. Attitudes, understanding and expectations of those around an individual and adaptations in society and everyday environments are fundamental to supporting meaningful participation and positive mental health in autism [16].
For the purposes of this review a psychiatric disorder is defined as a mental illness diagnosed by a mental health professional according to diagnostic criteria [17]. Relevant diagnoses were identified according to search terms and strategies described by Cochrane Common Mental Disorders [18].
There is limited understanding of effective interventions for supporting mental health in autistic adults [2]. A recent umbrella review found that research evidence did not support one best intervention for autism in children, and that there was a concerning lack of consideration of adverse effects of interventions [19]. Previous research has focussed on children and adolescents, often evaluating interventions designed to reduce or mask behaviours associated with autism [20] but there is now recognition of the stress and detriment such interventions can create [20,21]. The 'neurodiversity' movement considers autism and other neurodevelopmental conditions as neurological variation, rather than disorders requiring treatment [2,22,23], Therefore, autism is a difference not a deficit, which brings into question the use of interventions which seek to 'cure, fix or normalise' [2]. This movement has provided tools to critique research and to consider what is important in research and practice for autistic adults [16,23,24]. This has led to the development of research priorities which focus on the best interests of autistic people and recognise that the inclusion of both autistic people and non-autistic people in research processes is of key importance [22]. Although, there is a need for progress as only 5% of funded autism research included autistic adults [25]. Historical research must be reviewed through a contemporary lens which considers the acceptability of terminology, interventions, supports and outcomes to the autistic community [23]. Research indicates that autistic people prioritise outcomes associated with quality of life, reduction in anxiety, depression or sleep related problems, social well-being, interpersonal relationships, and increased participation in activities of daily living, community, and work [24].
These measures are key to evidence-based practice which requires the integration of the best available research with clinical expertise and the patient's unique values and circumstances [26,27]. Evidence based practice requires that health care is not only based upon the best available, valid, and current evidence as defined by GRADE (Grading of Recommendations, Assessment, Development and Evaluation) [28], but also that decisions are made by those receiving care and informed by those providing care [27,29]. Strong GRADE evidence indicates all or almost all people would choose that intervention [30]. This umbrella review of interventions will therefore consider the results of studies not only in terms of their effectiveness, but also regarding the acceptability of the interventions to the autistic community [23].
The prevalence of psychiatric disorders in autistic adults will be explored through rapid review of published literature. This knowledge synthesis will be rigorous and transparent but will be accelerated by resource-efficient methods including limiting the number of databases which will be searched for evidence. Handsearching, and forward and backward citation searches will also not be undertaken [31]. Grey literature, and literature not published in English will not be considered. Article screening will be reviewed by two authors in 20% of publications.
An umbrella review facilitates a synthesis and appraisal of evidence across a broader topic area than can usually be achieved through an individual systematic review [32]. In the current research, the aim was to incorporate these key viewpoints, integrating perspectives on evidence-based practice, and views from people with lived experience, experts, and practitioners. These key ideas are summarised below.

Objectives
We conducted a rapid review of existing studies providing quantitative data on the prevalence of psychiatric diagnoses in autistic adults. We also conducted an umbrella review of systematic reviews of interventions for autistic adults [32]. In both cases following Preferred Reporting Items for Systematic review and Meta-analyses (PRISMA) guidelines [33] (S1 Checklist). Our research was commissioned to inform an adult autism government policy review in Scotland which aimed to set priorities which are driven by autistic people. Considering these principles, our objectives for this review focussed on autistic adults were to: 1. Establish prevalence of psychiatric diagnoses and explore associated heterogeneity.

Investigate evidence for effectiveness of interventions.
3. Consider the acceptability of interventions and research in this field with reference to the neurodiversity paradigm.
Research questions.
1. How prevalent are psychiatric diagnoses in autistic adults?
2. Which factors are associated with heterogeneity of prevalence of psychiatric diagnoses in autistic adults?
3. Which interventions are effective in treating autistic adults?
4. Do available interventions meet the needs and priorities of autistic adults?

Methods
The systematic review process was undertaken in two parts focussing on (a) primary prevalence data describing the occurrence of psychiatric diagnoses in autistic adults; and (b) umbrella reviews of interventions. This was a rapid review, and to reduce the time required limited databases were included in the searches, and the umbrella review of interventions considered systematic reviews only, due to their higher quality research design [34,35]. Search date was restricted to 10 years as this is a valid and reliable approach for rapid reviews [36]. The protocol was registered a priori (PROSPERO #CRD42021283570).

Inclusion criteria
For both reviews, studies were included if: a) participants were autistic (however defined in the study which may include self-diagnosis or clinical diagnosis) b) participants were �18 years of age (or the mean age of the participant group �18 years) c) they were reported in English; d) they were published from 01/2011, AND 1. For the investigation of prevalence of psychiatric diagnoses in autistic adults; studies were included if they reported primary prevalence data for occurrence of psychiatric diagnoses experienced by autistic adults. OR 2. For the umbrella review of interventions; studies were included if a) they considered interventions for autistic adults; b) they were systematic reviews.

Search strategy
A systematic search of MEDLINE, CINAHL (Cumulative Index to Nursing and Allied Health Literature) and PsycINFO databases was conducted in November 2022, through EBSCOhost to identify quantitative studies of psychiatric diagnoses in autistic adults using Medical Subject Headings (MeSH) and keywords. To identify systematic reviews of interventions, a systematic search of CINAHL, MEDLINE, PsycINFO, and Cochrane Database of Systematic Reviews was conducted in November 2022. Databases were selected from available resources following current guidance [37], and through discussion with the university research librarian. CENTRAL, MEDLINE and Embase (if access to Embase is available to the review team) are recommended for systematic reviews [37-39]. Embase was not available to the research team. Cochrane Database of Systematic Reviews was included as a major repository of systematic reviews [32]. Trials searches of JBI Database of Systematic Reviews and Implementation Reports did not reveal any additional relevant citations and was therefore excluded. Lists of search terms are included (S1 File).

Study selection
Retrieved citations were uploaded to Covidence [40]. Following removal of duplicates, titles and abstracts of the returned articles were examined blind by two researchers (EC, NJ) with irrelevant titles excluded. Full text articles were then reviewed against inclusion criteria (EC), with 20% examined by a second reviewer (NJ). Disagreements were resolved through discussion, and reference to a third party (MR) was not required. Inter-rater agreement was assessed using Cohens Kappa.

Data extraction
Data extraction sheets were developed and piloted by two researchers. For prevalence, extracted data included study details, setting, sample size, age, method of diagnosis, prevalence data for: any psychiatric diagnosis; anxiety; depression; psychosis; schizophrenia; obsessivecompulsive disorder; attention deficit hyperactivity disorder (ADHD); bipolar disorder; eating disorder. For interventions, extracted data included study details, methodology, aims, population age and gender, context, inclusion/exclusion criteria, intervention, psychiatric diagnosis, autism diagnosis, sample size, subgroups, views of autistic adults, concerns re acceptability of intervention, conclusions, recommendations, funding sources. Data extraction was conducted by one of the research team members, then reviewed by the research team as a group, inconsistencies were resolved through discussion.

Evaluation of risk of bias
Studies included in the prevalence review were assessed for risk of bias using the Prevalence Critical Appraisal Instrument [41]. This assessment focusses on a) method of identification or diagnosis of the relevant condition, and b) sampling of the population, as these are issues particularly relevant to prevalence. Studies included in the intervention review were assessed for risk of bias using AMSTAR2 [42]. This tool identifies domains critical to integrity of the study, including registration of protocol (Q2), adequacy of literature search (Q4), justification for excluding studies (Q7), risk of bias in inclusion of studies (Q9), selection of meta-analysis methods (Q11), consideration of risk of bias in interpretation of results (Q13), consideration of publication bias (Q15). Studies are rated as high, moderate, low, or critically low according to the number of weaknesses identified [42]. Risk of bias was assessed by one member of the research team, then reviewed by another.

Synthesis methods
For synthesis of prevalence, studies were pooled according to psychiatric diagnosis.
For synthesis of interventions, results were grouped into pharmacological interventions; employment focussed interventions; psychological therapies; and mixed intervention or approaches. Within these broad categories, a list of detailed intervention sub-categories was identified. Next, evaluation of the strength of evidence for each sub-category was completed based upon the following criteria adapted from GRADE [28] from 'not recommended-to 'evidence based' (Table 1).
Interventions were evaluated against the stated adapted GRADE criteria to determine not only evidence of effectiveness, but also evidence of negative consequences or harm. This involved consideration of reported benefit for each intervention type. An exploratory approach was used to review adverse outcomes identified during the conduct of the review. This opportunistic approach considers only the reported adverse effects or outcomes that may be associated with the interventions being investigated [43].
In considering negative consequences or harm associated with interventions we included criteria adapted from clinical guidelines and neurodiversity affirming practice. Specifically, we did not recommend: • Interventions which focussed on the reduction of core features of autism are associated with harmful consequences and contradict current clinical guidelines [44,45]. Core features Table 1. Research recommendation classification.

Level of evidence Description
Not recommended There is no evidence of effectiveness, or there is evidence of negative consequences or harm

Unestablished evidence
All studies showed no effect or there was only one study with that intervention available for review Emerging evidence Two or more RCTs of lower quality, less rigorous study design and available evidence showed some or no effect, with no negative effects Evidence based Two or more high quality RCTs to support the intervention or five high quality single subject design studies conducted by at least three different research groups include qualitative differences and impairments in reciprocal social interaction and social communication, restricted interests and activities, and rigid and repetitive behaviours [46].
• Interventions associated with adverse events or adverse outcomes [43].
• Interventions which attempt to 'cure, fix or normalise' autistic people [2,47] due to their negative impact upon quality of life [29].
The research team was made up of autistic and non-autistic professionals within speech and language therapy, psychology, psychiatry, occupational therapy, and teaching fields. Members of the team had research experience, and experience working with autistic people in clinical and education settings. As integrated members of the research team, autistic researchers contributed to the planning and design of this research study, and decision-making related to study outcomes alongside non-autistic colleagues. All team members held professional roles and contributed expertise to the study thus possibly reducing issues associated with power hierarchy sometimes found in autism research [51]. Arising disagreements concerning the classification of evidence were resolved through team discussion with reference to research recommendation classification (Table 1) and criteria regarding negative consequences or harm listed above until agreement was achieved. Inter-rater reliability was not recorded for this process.

Results
The database searches returned 283 papers for the prevalence review and 448 papers for the interventions review. Of these 20 papers describing the prevalence of psychiatric diagnoses for autistic adults (Fig 1), and 32 papers describing interventions for autistic adults (Fig 2), met the inclusion criteria. Citations for excluded papers are provided (S2 File).
Cohen's kappa of inter-rater reliability was 0.70 for both studies, indicating substantial agreement between reviewers.

Prevalence
Characteristics of included papers relating to prevalence are described (Table 2), together with a summary of issues highlighted during completion of the Prevalence Critical Appraisal Instrument [41]. Studies often included small sample sizes or failed to compare their sample group with the general population reducing understanding of the validity of their findings. Prevalence data was not pooled due to heterogeneity [52], which was associated with age, cooccurring conditions, sampling method, mode of diagnosis, variation in the categorisation or grouping of diagnoses, and the country in which the study took place. Prevalence ranges, across all studies, locations, and lifetime vs current diagnosis, were any psychiatric diagnosis 15%-79%; Attention-deficit hyperactivity disorder 2%-33%; Depression 10%-54%; Anxiety 10%-54%; Psychotic disorders 0.2%-18%; bipolar disorder 1%-25%; obsessive compulsive disorder 2%-33%; and eating disorders 2%-11% (Table 2).

Interventions
Characteristics of the systematic reviews relating to interventions for autistic adults are described in Table 3. This includes effect size from any data synthesis conducted within the   reviews. Five reviews were focussed on pharmacological interventions, nine examined employment focussed interventions, seven reviewed the evidence for psychological therapies, and the remaining 12 explored evidence for mixed interventions and approaches. Critical appraisal was conducted using AMSTAR2 [42]. Four reviews were rated high, four were moderate, five were rated low and 18 critically low, indicating strong risk of bias (see Table 3). Exceptionally, one paper described the inclusion of autistic researchers within the research process [71]. This study included a community council comprising 18 people who mostly identified as autistic or were the parent of an autistic adult, and were researchers, medical or  mental health professionals, authors, or advocates. This council reviewed study results and contributed to study recommendations [71]. Heterogeneity in outcome measures and variation in the content, length, and delivery of interventions prevented pooling. Outcome measures were often not referenced adequately to permit investigation into their reliability or validity for this population. Full name and authors of outcome measures where reported are included in S3 File. Reviews did not always report results of individual outcome measures and often used diagnostic assessment tools as outcome measures which are not only insensitive to change but indicate a focus on the reduction of core autistic features [72]. Few interventions were manualised, and there was limited reporting on the training, skills, or experience of practitioners.
Summary of evidence for effectiveness and acceptability of interventions. The summary synthesis of intervention sub-categories with GRADE recommendation is presented in Table 4. There was considerable overlap in the primary studies reported within the retrieved

PLOS ONE
systematic reviews (S4 File) which prevented further data synthesis. Column 3 of Table 4 outlines factors which may impact the acceptability of interventions to autistic adults including research limitations, indications of adverse effects, adverse outcomes, or priorities contradicting those identified by the autism community. Overall, results indicate a need for further robust research. None of the included interventions were rated as 'evidence based', and eight were 'Not Recommended.' There was 'Unestablished' or 'Emerging Evidence' for the remaining interventions.
Pharmacological interventions. Five reviews [81,88,89,98,100] considered 139 studies evaluating pharmacological intervention for autistic individuals. One review was high quality (Table 3). Managing behaviours with medication as a first line of intervention or using medication including SSRIs (Selective Serotonin Reuptake Inhibitors) or Oxytocin for core features of Autism is not recommended (Table 4) [46,100]. However, there was emerging evidence for use of medication as a last line of intervention. Oxytocin may offer some benefit but did not

Autism
Mixed, NE, Results suggest job interview training may be effective in improving interview performance, social skills training can be effective in improving self-rated social skills, autism symptoms and social relations; and employment programmes can be effective in increasing employment for autistic adults without ID. The evidence for other interventions and outcomes is inconclusive and limited.
It is unclear how outcomes such as improved mock interview performance might generalise to real world outcomes. L (Continued )

PLOS ONE
Mental health in autistic adults affect global clinical status [88]. Risperidone may be useful in the management of repetitive, aggressive, and self-injurious behaviour [81], although side-effects are problematic [98]. There was limited evidence to support the use of opioid antagonists to reduce self-injury in autistic adults [89]. However, fluoxetine or fluvoxamine may be useful in the management of repetitive and obsessive-compulsive behaviour and anxiety where other interventions are not available or possible due to the individual's level of distress or aggression [98]. Overall, there is a need for future research to consider the acceptability of pharmacological interventions including further investigation of side-effects. Employment focused interventions. Nine reviews of evidence for employment focussed interventions considered 100 unique publications [78, 80, 82, 83, 85-87, 90, 97]. None of the reviews were high quality (Table 3). Reviews revealed emerging evidence that supported employment including Individual Placement Support (IPS) and Project Search, yields positive outcomes for autistic people [78,80,82,86,87,90,97]. Notably, autistic adults, undertaking Project SEARCH with autism support were eleven times more likely to achieve employment than those attending special education [87]. However methodological concerns mean this result must be interpreted with caution as studies did not include comparable control groups or consider participant attrition [78]. Evidence for technology-supported interventions such as virtual reality training was unestablished as the relationship to paid employment was not confirmed [85]. Employment related social skills training research often focussed on alternative outcomes to employment status, such as interview skills performance, and therefore the evidence for such an approach is unestablished. Sheltered workshops were not recommended as they were not associated with supporting autistic people into employment but could provide other benefits. Further research is required to consider the impact of employment focussed interventions not only on employment status and wage, but also on quality of life [24].
Psychological therapies. There were 7 reviews of psychological therapies including 215 studies [74,75,79,[93][94][95]99]. Only one review was of high quality ( Table 3). The reviews revealed emerging evidence (Table 4) for the use of mindfulness for the reduction of selfreported depression symptoms in autistic adults without intellectual disability [71,79,84]. Studies provided emerging evidence for use of Cognitive remediation therapy to improve cognitive function, but small sample sizes and limited follow-up made it difficult to determine meaningful impact or maintenance of any benefit in the longer term [75].
There was unestablished evidence for the use of cognitive behavioural therapy (CBT), although small positive clinical effects on self-reported outcomes were observed [71,99]. Within nine systematic reviews, which included CBT studies, 11 different types of CBT were described and included CBT combined with other interventions including behavioural techniques, mindfulness, and psychoeducation [93,94]. These major variations in the intervention provided meant it was not possible to conclude this intervention was effective. Additionally, there were expressed concerns regarding CBT which are outlined in Table 4 and which should be considered in future research.
There was unestablished evidence for family therapy due to limited quality research [95] although non-randomised intervention studies suggest there may be improved knowledge and understanding of core disorder (ASD), and coping styles post-intervention [95]. Acceptance and Commitment Therapy was not recommended due to limited research and insufficient rigour [74] to suggest ACT is effective in the management of psychological distress for individuals with ID [74].

Intervention GRADE level Acceptability Pharmacological
There was no consideration of the acceptability of these interventions to autistic people. One review commented that the autistic community report that medication side-effects and dosing are not well evaluated, and that medication generally, is poorly tolerated [71].
Managing behaviours deemed problematic, with medication, as a last line of intervention

Emerging evidence
Medication may be used to address co-occurring conditions, such as anxiety, self-injury, OCD, or depression [46].
Medication for core features of Autism Not recommended Contradicts current guidelines [46].
Managing behaviours deemed problematic, with medication, as a first line of intervention Not recommended Contradicts current guidelines [46].

Employment focused
Generally, studies of vocational or employment interventions did not consider health outcomes, or impact on quality of life for autistic adults [71].

Project SEARCH Emerging evidence
Project Search and other supported employment models are promising models for helping people attain employment, but further research is required.

Individual Placement and Support (IPS) Emerging evidence
Further robust research is required.

Supported Employment Emerging evidence
Cost benefit of supported employment is not known. Some studies reported employee job satisfaction [86].

Technology supported interventions Unestablished evidence
Technology supported interventions are under-researched and have focussed on proximal measures to employment status e.g., improvement in interview performance, rather than employment outcomes.

Employment related social skills training Unestablished evidence
There is a need to demonstrate the link between these outcomes and employment.

Sheltered workshops
Not recommended No evidence that sheltered workshops support people into employment. They may support other outcomes.

Psychological Therapies
Psychological therapies can be used, but with caution, as there is insufficient evidence of their effectiveness over other approaches. There is a lack of evidence over which autism adaptations should be incorporated and how this should be done [90].

Mindfulness Emerging evidence
Need for more robust research evidence.

Cognitive Remediation Therapy Emerging evidence
Need for more robust research evidence CBT Unestablished evidence CBT is not significantly better than alternative interventions and autism adaptations are insufficiently researched [90,102]. Self-report measures are not reliably associated with significant change following intervention because autistic people may have developmental differences in communication and perspective taking which leads to difficulty reliably reporting symptoms [12,93,94]. Reliability and validity of most administered questionnaires has not been established for autism community [93]. Clinical diagnoses in most studies were established using standrad diagnostic criteria despite overshadowing of some mental health diagnoses and autism [93]. There was a wide range of experience with each intervention. One review stated some autistic people report that CBT is unhelpful for them [93]. There is a need for evaluation of long-term impact of CBT interventions [71]. Studies reported effectiveness of CBT for symptoms associated with autism in contravention of current guidelines [99].
Acceptance and Commitment Therapy (ACT) Not recommended Limited research and insufficient rigour [74].

Mixed interventions/approaches
Caution is required to ensure interventions do not aim to "cure" autistic traits [44].

Program for the Education and Enrichment of Relational Skills (PEERS)
Emerging evidence The PEERS approach is acceptable to autistic people where care is taken to avoid shaming non-neurotypical communication styles [68].

Social cognitive interventions Emerging evidence
There is a need to engage with the autistic community about the concept of theory of mind for describing differences in noticing and interpreting intention, thoughts, or beliefs of others. Additionally, there is a need for clarity about when, why, or how such interventions might be relevant.
(Continued ) emerging evidence for the use of the PEERS programme in reducing social anxiety and loneliness [20]. Although, concerns regarding social skills interventions including PEERS includes the risk they teach camouflaging which has been associated with suicidality [71,103]. There was also emerging evidence for social cognitive interventions [73,83] although there is a need to explore whether these interventions are required by the autism community. There was unestablished evidence for social skills interventions [20,77,83,84,92,101] and studies were criticised for their limited input from autistic people instead relying on parent or caregiver reports [20], Results indicate positive effects from communication interventions [20,83,101] but there is a need for additional robust research. Music, and dance therapies research did not demonstrate the effectiveness of this type of intervention [72,83]. Music therapy intervention studies suggest this may have a positive impact on autistic children regarding social interaction and communication, although studies did not find significant difference in symptom severity [72]. These studies relied heavily on diagnostic measures to analyse social or behavioural differences before and after intervention [72]. Diagnostic measures are generally insensitive to change and indicate a focus on the treatment of core symptoms. There were no randomised controlled trials investigating the impact of music therapy. There is also a need for further robust research investigating the benefits of environmental, leisure and participation focussed interventions [20,71,73,76,83]. Evidence for behaviourist approaches was unestablished [71,73,76,101]. Although, the

Social skills interventions Unestablished evidence
There is a need to engage with the autistic community in relation to strengths-based approaches within social skills interventions to ensure that they are not trying to 'fix' or 'cure' individuals [20]. Social skills are important for relationships however, some autistic people see some social skills interventions as teaching camouflaging, which has been associated with suicidality [71,103]. Some social skills interventions present specific behaviours relating to autistic features as wrong which can be detrimental to the health or identity of autistic people [71]. Reported study feedback includes statements that interventions were helpful [20]. Another study reported participant feedback that social skills groups were acceptable, and they were able to put some of the skills into practice. Reported attrition rates ranged from 10-18% [92]. There have been concerns raised regarding Applied Behaviour Analysis (ABA) by autistic adults and further engagement with the autistic community is required to reach a shared understanding about whether or not these approaches should be used [21].
Electro-convulsive therapy (ECT) Not recommended ECT is not recommended as there is evidence of a negative response to this intervention and of high risk of bias in research studies [68] Major concerns about this intervention include possible damage to brain and memory [71].
Group academic and social skills training Not recommended There is a need for further research regarding the suitability of social skills interventions for reducing secondary effects of social skills impairments [92].

Movement based interventions
Not recommended Limited research.
Auditory integration training (AIT) Not recommended Questions have been raised regarding the potential of AIT to risk hearing loss [91]. A statement issued by American Academy of Paediatrics endorsed the lack of benefit of AIT [91]. autistic community have expressed concerns regarding the use of applied behaviour analysis and further engagement is required to determine whether these approaches should be used [21]. Electro-convulsive therapy was not recommended, and autistic researchers involved in the systematic review did not feel this was an appropriate intervention for autistic people [71]. There is evidence of negative responses to this intervention and of high risk of bias in research studies [71]. Major concerns were expressed about this intervention including possible damage to brain and memory [71]. Auditory Integration Training was not recommended due to absence of evidence, and safety concerns [91]. Group academic and social skills training [84] were not recommended. Group social skills interventions were more effective for enhancing knowledge and understanding, rather than increasing specific social skills [92]. Acceptability to the autistic community in retrieved studies. One systematic review, exceptionally, reported including autistic individuals and families who checked results, recommendations, and acceptability of interventions [71]. Evidence for interventions aimed at the reduction of core features of autism were not recommended, Intervention studies were limited by restricted reporting of outcome measures, or use of outcome measures not validated for autistic adults.

Discussion
Improved understanding of the relationship between individual characteristics and mental health in autistic adults is required to target interventions. Our review of studies exploring the occurrence of mental ill-health in autistic adults revealed wide variation in prevalence associated with means of diagnosis, age, co-morbidity, and country of residence. Study populations included higher proportions of male participants reflecting the historical gender imbalance in autism diagnosis.
We identified prevalence of psychiatric diagnoses in autistic adults. Attention-deficit hyperactivity disorder (2%-33%); Depression (10%-54%); and Anxiety (10%-54%) were most common. Population-based studies reflecting lifetime diagnoses identified higher prevalence than current diagnosis studies. Prevalence of mental health related diagnoses was higher in studies which used clinical samples. Most studies included smaller samples. Clinical studies may mean greater chance of clinician and service contact, raising chance of diagnosis for individuals. Diagnoses in clinical populations are also more likely to conform to identified diagnostic criteria.
This rapid review supports previous findings that age was associated with heterogeneity in prevalence of psychiatric diagnoses [1]. Autistic people over the age of 65 were more likely to report a lifetime mental health condition than autistic people aged 55-65, although this pattern was not found when examining current diagnoses [63] possibly due to additional time available to experience mental ill-health. Age related differences may be due to changes in diagnosis patterns and criteria over time, or to the reduced life expectancy of autistic people [59,60]. Additionally, autistic people with intellectual disability are more likely to experience mental illhealth, than people with either intellectual disability or autism alone [8]. Prevalence of psychiatric diagnoses in autistic people also appears higher for people living in USA than UK [61,62].
Prevalence may also be influenced by the lack of diagnostic tools validated for the autistic community, and which may be unable to discriminate mental ill-health from autistic features resulting in diagnostic inaccuracy or overshadowing [12,60]. Self-reporting, and the varying ability to report internal emotional experiences, may also impact diagnostic accuracy [12].
The use of resource efficient methodologies may have reduced the number of prevalence studies revealed during this rapid review [31]. However, search strategies focussed on the identification of research aimed at identifying the prevalence of psychiatric diagnoses in autistic adult population rather than in small purposive samples. The sampling of the population within prevalence studies is particularly important [52]. Therefore, studies which examined small purposive samples which were not compared with the wider population, were less likely to be representative of the general population.
The umbrella review revealed evidence across 31 systematic reviews relating to interventions for autistic adults, but no intervention was rated 'evidence based' and several interventions were 'not recommended.' A key issue was acceptability to the autistic community. Reviews mostly failed to consider the views of autistic adults or include autistic adults in planning or conducting the research. One systematic review, exceptionally, included autistic individuals and families who checked results, recommendations, and acceptability of interventions [71]. Research rarely focussed on the identified priorities of the autistic community which include interventions focussed on skills development and training from childhood; employment; physical health, wellbeing; mental health; and expertise, coordination, availability, and accessibility of lifespan services [48]. It should be noted that these priorities may not reflect the views autistic people who are minimally verbal.
Despite the availability of knowledge on priorities according to autistic people, the identified research mostly reflected changes to the autistic person including the development of social skills, and the reduction of 'symptoms' associated with autism or behaviours deemed undesirable. Such behavioural and psychological interventions have been criticised for aiming to remediate aspects of autism resulting in stress or harm for autistic people rather than focussing on outcomes identified as meaningful [49]. Reviewed studies incorporated a wide range of outcomes which were measured using heterogeneous tools with little discussion of their relevance to priorities identified by the autistic community. This has implications for the interpretation of the results, as measured outcomes may or may not be meaningful to autistic people and reflects the limited range of assessments validated for use with autistic adults [12].
Employment was considered in many studies and has been identified as a research priority by the autism community [48] as autistic adults are often excluded from participating in integrated competitive employment. However, studies often failed to report outcomes directly reflecting employment status following intervention [104], instead reporting outcomes such as improvement in interview skills or cognition, which may or may not support people in achieving employment. This may be due to limited follow-up after the intervention concluded. Other studies examined complex work programmes making it difficult to identify the 'effective' components.

Implications
Further high-quality research must be designed with the autistic community focussing on their needs and priorities. Improved understanding of processes for matching individual needs and preferences with evidence-based interventions is required [3,50]. Interventions offered to autistic people should take account of the person's preferences, needs and communication differences, and the impact these may have upon mental health [105]. Research must consider the benefits of interventions which focus on individual communication, sensory or thinking preferences. Interventions which consider adaptations to the environment must also be prioritised [50].
Staff and organisations, including health staff, adult mental health practitioners, and human resources/employment specialists, should consider what support can be offered in workplace environments [50,71]. There are significant training needs in the workplace. This includes training needs of autistic people and non-autistic people. Reviews particularly identified transition into employment as a key time requiring focussed attention [14].
The findings of this review suggest that practitioners and organisations who support autistic adults with their mental health should prioritise individual needs and consider focussing on approaches to building self-understanding of individual neurodevelopmental profiles before (or in conjunction with) talking therapies [71]. Ideally, practitioners should be part of a multidisciplinary team and should not only have training in approaches or therapies but have experience in working with autistic people, assessing communication support needs, and understand alternative supports and adaptations for autism [48,49,71]. Intervention decisions should take account of autistic people's individual preferences and needs, their day-to-day environments, neurodevelopmental and particularly communication differences, and the way sensory, communication or thinking preferences might impact on their mental health [14,49]. Such approaches could address the current tendency to focus on people's difficulties rather than consideration of environmental supports and individual needs [49,50].

Inclusion of autistic people
Autistic researchers were an integral part of the research team which conducted this review and were included throughout the rapid review and umbrella review process. The team provided critique of evidence for interventions which could potentially be detrimental to autistic people, including encouraging the expression of neurotypical behaviours which is a form of masking. Papers were examined for the inclusion of autistic researchers, and for views expressed by autistic people on the acceptability of interventions.

Limitations
Rapid review methodologies were used [34]; including date and language restrictions, limiting the number of databases that were searched, and focussing on systematic reviews of intervention studies. The research team did not have access to EMBASE which is recommended for intervention reviews where available to researchers [37]. While the review team completed a comprehensive search using recognised methods no forward or backward citation search, hand searching or follow up with authors was completed to identify missing studies. These methods and the selection of databases used in the search may have contributed to the low number of studies identified. The intervention research displayed very high heterogeneity across included studies, interventions used, and outcome measures applied. An exploratory approach to reviewing adverse effects considers only reported information, and is therefore restricted by incomplete reporting, or inadequate monitoring of adverse outcomes. Separate searches for adverse effects of interventions were not conducted and therefore results are unlikely to be comprehensive [43]. Retrieved studies did not declare that they did not include autistic researchers and research teams may therefore have included autistic researchers. Autistic researchers were integral to the research team conducting this study and their views were not recorded separately from other research team members. Autistic research team members have professional backgrounds within research, health and education and are therefore not representative of all sections of the autistic community.

Conclusions
There is limited understanding of mental ill-health and how this can impact quality of life for autistic people despite evidence indicating increased prevalence. There is a need for diagnostic tools and outcome measures to be validated for use with this population. Future research should fully include autistic people at every stage and focus on priorities identified by the autistic population.